1. Field of the Invention
The present invention relates to the field of self-powered apparatuses and tools, more particularly power autonomous portable electric tools, and relates to a lithium-ion or polymer lithium battery-operated tool set of the aforementioned type.
2. Description of Background Information
In the present invention, “tool” is generally defined as an apparatus or implement adapted to facilitate the physical work of an operator performing a task, or to perform said task while controlled by an operator. By “tool set” is meant a tool and its autonomous rechargeable electric energy source, and the device for supplying the latter.
The following tools, which have already been manufactured by the Applicant, can be cited: electronic pruning scissors for cutting fruit trees and vineyards, vegetable grafters and fruit picking tools.
Other tools, manufactured using similar techniques, can be cited in a non-limiting manner among tools of the aforementioned type, including: saws, lawnmowers, bush cutters, hedge cutters, impact spanners, pneumatic hammers.
These power portable electric tool sets essentially distinguish over comparable tools that are actuated by hydraulic, pneumatic, and electric power sources in that they are self-contained and independent of any external power source, which enables the operator to move freely. They also distinguish over self-contained heat engine-powered portable tools, by the lack of pollution, foul odors, vibrations and noise during use, as well as by their reliability of use.
Furthermore, it has been shown that the use of these tool sets provides an unprecedented comfort of use, due to their silent operation and their flexibility.
Such power autonomous portable electric tool sets generally include at least three distinct functional sub-units, namely, a first sub-unit forming an electric actuator and generating the mechanical operation of the tool, a second sub-unit forming an electric energy source and essentially including a rechargeable electrochemical battery, and a third sub-unit forming a charger capable of recharging the battery.
The advent and development of these tool sets are mainly linked to two technical factors:
the commercial availability of new types of batteries having a better capacity to weight ratio, on the one hand; and
the development of technologies producing high performance electric motors.
The batteries that are currently used in the aforementioned tool sets are of the nickel-cadmium type, or of the nickel-metal hydride type. They have an energy capacity of about 30-50 watt-hour per kilogram.
Knowing that an operator is allowed to carry a maximum of 4 kg on his back, across his shoulder, or on his belt for work sustained throughout the day, in compliance with official guidelines, one can infer that with the current techniques using nickel-cadmium and nickel-metal hydride, the total capacity of the battery carried by the operator is between 120 and 200 watt-hours.
This capacity is not always sufficient to provide the power autonomous portable electric tool sets with the energy required to operate half day, let alone a full day.
Therefore, there is a need and an actual demand for batteries having a more efficient capacity to weight ratio, in order to expand the field of application of the power autonomous portable electric tool sets, in view of their aforementioned advantages and qualities.
To this end, the invention aims at using the emerging technology of lithium-ion and lithium polymer batteries in the context of power autonomous portable electric tools.
Indeed, although these batteries are now frequently used in mobile telephones, video cameras, and portable computers, they are not yet used in applications to portable electric tools, especially professional grade tools, due to difficulties encountered with their implementation in application requiring a lot of power and autonomy. However, they currently offer capacity to weight ratios of 150-220 watt-hours per kilo, which would triple, or even quadruple the power or operating time of these portable electric tools, compared to their current capabilities when used with nickel cadmium or nickel metal hydride batteries.
It should be noted that due to the power requirements, the use of lithium-ion and lithium polymer batteries in power portable electric tools requires high voltages.
Indeed, the lithium-ion and lithium polymer elements cannot naturally deliver too high a current and therefore require the base elements to be serially coupled so as to obtain high voltages, thereby making it possible to supply adequate voltages, in spite of a limited current.
Thus, to form batteries that deliver electric power adapted to applications to power autonomous portable electric tools, while complying with the laws in force governing serviceable voltages and providing useful working voltages, it is necessary to serially couple numerous elements or numerous cells, each of these cells grouping such elements in parallel.
By “element” is meant an individual electric energy accumulator. The lithium-ion or lithium polymer base elements are industrially manufactured according to standardized formats adapted to the applications. They are produced in bulk, at very competitive costs. Advantageously, but in a non-limiting manner, the elements of the lithium-ion battery of the second sub-unit described hereinafter are in the commercial 18650 size that offers the best capacity to cost ratio. As a general rule, these elements are equipped with internal safety mechanisms which enable high capacity batteries to be used safely.
As a result, there are substantial difficulties in controlling and/or managing such multi-component batteries, which have yet to be resolved.
Indeed, in the aforementioned applications (mobile telephones, video cameras, and portable computers), the batteries generally comprise at the most four serially associated elements or cells, the control of which, when charging and discharging, is not complex and is relatively easy to implement.